The present invention concerns the manufacture of electric motors and generators, and similar apparatus. More specifically, the invention relates to improved solutions for winding stators for dynamo-electric machines.
Electric motors generally include two main parts--a fixed hollow portion known as a "stator" and a portion that rotates inside the stator, called a "rotor" or an "armature." Electrically conducting coils of wire are typically wound in longitudinal slots on the terminal board portion of the stator. Rotors are configured in many different ways, but they are also wound with electrically conducting wire. Current supplied to the rotor wires interacts with a magnetic field that is produced in the stator to create the torque required to operate the motor. Electrical generators have stators and rotors that are similar in a general way to those described above for electric motors.
Various types of machines are available to form windings on stator cores. Some machines include needles, driven with rectilinear reciprocating motion combined with reciprocating rotary motion about their axes, to carry copper wire from a reel and place it in the stator slots. In one such device, the needle is aligned coaxially to the central axis of the stator. Because this configuration fails to position the point of the needle such that the wire can be placed in all areas of the slot, "shrouds" or "shoes" are typically placed at the ends of the slots to guide the wire into proper position. More specifically, a retaining tooth is usually present at the end of the slot to support the portion of the wire that rests above the slot as winding proceeds. When a device such as that described above is used, the needle cannot extend far enough to bring the wire past this retaining tooth during winding. The wire emitted from the needle rides along the surface of the shoes and into proper position in the slot.
While using shoes to aid in winding is an acceptable solution, considerable effort is required to use them. For example, because the shoes occupy large amounts of space, particularly extending in the direction parallel to the longitudinal direction of the stator, the needle has to travel through a longer winding stroke in order to place the wire in position next to the shoes. Moving the needle through longer winding strokes substantially increases the amount of time that must be allotted to winding the stator, which is an undesirable result. Reaching the increased stroke distance also requires the use of a longer needle. Since winding needles are typically cantilevered from the actuator, longer needles are subject to additional flexion which must be countered by increasing the stiffness of the needle.
In addition, the appropriate size of the shoes must be chosen based upon the dimensions of the stator, and inaccurate shoe sizing can result in failed attempts to form the winding. Further, complicated mechanisms must be used to add and remove the shoes. This again adds a considerable amount of time to the winding process. Expending so much energy supplying devices that form no part of the final product is highly inefficient. Thus, it is advantageous to form windings on stator cores using a device that does not require the use of shoes.
Winding machines that do not require the use of shoes are available. In these devices, the needle is typically aligned within the stator such that it may position wire anywhere in the slots. One such device positions the winding needle such that its rotation and advancement axis is eccentric with respect to the central longitudinal axis of the stator. This type of device is disclosed in U.S. Pat. No. 4,991,782 to Luciani, issued Feb. 12, 1991 and assigned to the assignee of the present invention, the contents of which are hereby incorporated by reference in their entirety. In another device, the end of the needle has two opposing points, which are orthogonal to the needle. These needle ends diverge when the needle is external to the stator during its rotation, and then converge when the needle is inside the stator, to deposit wire in the slots. Such a device is disclosed in U.S. Pat. No. 4,762,283 to Sabatino (more accurately Luciani), issued Aug. 9, 1988 and in U.S. Pat. No. 4,858,835 to Luciani et al. issued Aug. 22, 1989 both assigned to the assignee of the present invention, the contents of which are hereby incorporated by reference in their entirety.
While such winding devices are quite useful in forming windings on many stators, they sometimes produce unacceptable windings. For example, winding stators that have slots spaced far apart often results in an unevenly distributed wire coil. That is, the wire tends to bunch up against the terminal board on the side where the needle exits the stator core, and to extend along the terminal board on the side where the needle enters the stator core. Uneven wire distributions are also sometimes produced when the gap between the ceiling of the slot and the surface of the coil holder that supports the coil is very small. These uneven windings reduce the overall slot fill capacity of the stator. Thus in addition to winding the stator without using shoes, it is also desirable to produce an evenly distributed winding.
In view of the foregoing, it is an object of this invention to provide improved methods and apparatus for placing an even winding on a dynamo-electric machine stator.
It is another object of this invention to place such even windings on the stator without using shoes to guide the wire into proper position.